A metal flap installed at the bottom of the bowl of a chemical or pit toilet, which blocks out unwanted odors. The flap is hinged and sprung in such a way as to only open when a certain amount of weight is applied to it.

A common accessory for this device is the stoker - a small stick which is used to manually operate the flap, should it for some reason fail to open.

"I say, Thomas, would you be so kind as to pass over a stoker, I have produced a rather large stool which has become lodged in the shit flap".